The warping is a technical problem commonly encountered in children’s board book printing. Now let’s talk about our views on this issue based on our years of practical experience.
Analysis of the warping for the board book printing
- Raw materials
The structure of a gray board or cardboard itself determines that it is easy to be warped in production. The density of grey board or cardboard is large, and the fiber is long. Its water absorption has a great impact on the structure of board books. When absorbing water, the fibers of the gray board or cardboard will stretch.
However, because the gray board or cardboard has a certain thickness, the water absorption capacity on both sides will be inconsistent, resulting in different elongation lengths of the gray board or card board fibers, which will cause the gray board or cardboard to deform.
At the same time, when water loss occurs, the fibers of the gray board or cardboard will shrink, but the inconsistent water loss on both sides will lead to inconsistent fiber shrinkage, resulting in deformation. Although the grey board or cardboard will be deformed due to water absorption and loss, from our years of production experience, the deformation caused by water loss is more serious than that caused by water absorption. In addition, different brands and models of grey boards or card boards have different water absorbency and different deformation phenomena in production.
- Ambient temperature and humidity
The environmental temperature and humidity have a great impact on the production of board books. When the ambient temperature and humidity are lower than the moisture content of the board, the board will lose water, and the degree of water loss of each part of the board is generally different, which will cause the board to rise. When the ambient temperature and humidity are higher than the moisture content of the board, it will cause the board to absorb water, which will also cause the board to warp. The degree of deformation under these two conditions is different. The deformation during water loss is far greater than that during water absorption, so the warping of board books always occurs in the dry season in autumn and winter.
- Production process
When printing board books, you need to use white latex to cover or mount. The white emulsion contains a lot of water. When the shell is mounted or mounted, a lot of water will enter the board paper, but the water does not enter evenly, which leads to inconsistent water content in all parts of the board paper, leading to the board book warping.
- Operation mode
During the production of hardcover books, some enterprises use the machine to automatically shell, while some enterprises use the manual shell. Generally, the adhesive coated with the machine to automatically shell is more uniform than the manual shell, making the moisture content of the board paper more uniform. At the same time, the viscosity of the adhesive used for automatic shell mounting of the machine is different from that used for manual shell mounting, that is, the solid content of the adhesive is different. The solid content of the adhesive used for automatic shell mounting of the machine is higher than that of the adhesive used for manual shell mounting, and the water content is smaller, which makes the card board book less prone to warping.
- Production process
Both the grey board and cardboard have lines, so when you mount the card board book on the shell or in pairs, you need to follow the lines. A lot of production experience tells us that for hardcover books, we need to cover them along the grain; For the book mounted in pairs, it needs to be mounted in parallel with the grain. If it does not follow the grain, serious warping will occur in the later period of the finished card board book.
These are the main reasons for the warping of custom board books in production. From the data obtained from mass production practice, it is ideal to control the moisture content of card board book within 8%~12%, and its warping can be well controlled.
How to improve the warping of board books
- Proper selection of raw materials
You need to select the gray board or paper jam with moderate tightness. Tightness is too small, the paper has strong water absorption. And is greatly affected by environmental temperature and humidity. So it is easy to deform. If the tightness is too large, other quality problems will occur. In addition, when using, we must ensure that it is parallel to the grain. That is, the grain of the gray board should be parallel to the direction of the book ridge.
The two pieces of card board mounted should be carried out according to the grain direction as far as possible (that is, the grain is parallel to the direction of the book ridge). So as to avoid the warping of the card board book caused by the inconsistent grain. In terms of adhesives, white latex with large solid content shall be selected as far as possible. And the mixing of two kinds of white latex shall be eliminated.
- Suitable production environment
The production environment should be kept moderately stable, that is, the temperature should be controlled between 20 and 30 ℃, and the humidity should be controlled above 45%. From April to September every year, the air humidity is generally above 50%, and the temperature can also be controlled at 20-30 ℃, so the warping of card board books rarely occurs. However, from October to March of the next year, as the ambient humidity is below 40%, or even lower, the quality problem of card board book warping often occurs. When the humidity is too low, it is necessary to spray a certain amount of water in the air of the workshop to keep the air humidity above 45%.
- Strictly control all production links
Before the production of hardcover books, it is necessary to take out the ash board from the warehouse at least 24 hours in advance. And place it in the production workshop. During the process of material opening, shell making and shell loading. The moisture content of the ash board before and after the process should be tested to ensure that the moisture content is 8% ~12%. For the card board mounted book, it is also necessary to take the card board out of the warehouse 24 hours in advance and place it in the production workshop. Before and after mounting, it is necessary to test the change in the moisture content of the card board. When the moisture content is higher than 12%, the card board needs to be dehumidified until it reaches 8% ~12%. During dehumidification, the paper jam needs to be fixed to prevent the paper jam from deformation due to water loss during dehumidification. It should be emphasized that in each control link, the moisture content of the gray board or card board should be tested, and the test results should be recorded for the purpose of summary, analysis, correction and prevention afterwards.
- Pay attention to packaging and transportation
The transportation of finished products after packaging is also very important. For domestic products, it is necessary to know the ambient temperature and humidity of the customer’s location and the factory’s location in advance. If there is a large difference between the two temperatures and humidity, it is recommended to shrink package the finished products. For foreign products, it is also necessary to know the ambient temperature and humidity of the customer’s location in advance. In case of sea transportation, it is also necessary to consider the temperature and humidity of the cabin during sea transportation. If the products are produced from October to March of the next year, it is recommended to shrink package all finished products. At the same time, it is possible to consider negotiating with the shipping company to place the product at the bottom of the cabin.